(fwiw, posted in Beta forum before I resigned as a tester and no longer have access to it)
Due to the excellent and sound-shaping flexibility of WACUP/Winamp, I strictly view all my mp4-based music videos with this app. Unfortunately, my experience with WACUP forces me to return to Winamp 5.666. My video library is typically 720/1080 and the playback (video, not sound) is very jittery and pixelated. Out-of-the-box Winamp video playback is smooth and crisp. dro and others have pointed me to various settings and adjustments to deal with my various issues with positive results so, hopefully, there may be a cure for this issue. I will remain with Winamp until this is resolved in WACUP. I first notice this in latest Beta. Went back to Preview Build release and confirmed this behavior there as well.
(If desired I can provide my 'test' video)
-thank you